1. Field of the Invention
The present invention relates to a transfer sheet guiding device adapted for use in an electrophotographic imaging apparatus, and more particularly to a transfer sheet guiding device for forcedly guiding and separating a transfer sheet from a latent image carrying member after the transfer therefrom of an electrostatic latent image or a visible image developed therefrom onto said transfer sheet.
The present invention further relates to a transfer sheet guiding device wherein a surface of the guiding means can be utilized as a so-called hot plate fixing device for heat fixing of an image on said transfer sheet.
2. Description of the Prior Art
Generally in an imaging apparatus utilizing electrophotography such an electrophotographic copier, there is provided an electrostatic latent image carrying member such as a drum-shaped photosensitive member provided with a photoconductive layer, and a reproduced image of an original is produced during rotation of said photosensitive member. In such apparatus there are provided charging means, exposure means and developing means along the periphery of said rotary photosensitive member, for producing an electrostatic latent image corresponding to an original image, said latent image being rendered visible by development with toner particles. The visible image thus obtained on the photosensitive member is thereafter transferred electrostatically onto a transfer sheet such as plain paper and fixed thereon for use. On the other hand the photosensitive member, after said transfer, is cleaned of remaining toner particles in preparation for the next imaging cycle.
At the above-mentioned transfer it is generally necessary to apply an electric field, by a voltage applying means such as a corona discharger or a roller electrode, in order to transfer the developer, or toner particles, onto the transfer sheet. This is usually achieved with a corona discharger by providing the transfer sheet with an electrostatic charge, which strongly attracts the latent image on the photosensitive member, resulting in an electrostatic intimate adhesion of the transfer sheet to the photosensitive member. Such adhesion is indispensable for transfer of toner particles without distortion to the transfer sheet during the transfer process. After the completion of said transfer step, however, it becomes necessary to forcibly separate the transfer sheet from the photosensitive member by means of suitable separating means in order to advance said transfer sheet to the fixing means. For such separating means there are already proposed a vacuum suction method and an air blow method in which compressed air of an elevated pressure is blown from blowing means such as a nozzle. Such air-operated separating mechanisms, however, inevitably involve a compressor or a pump and pipes for guiding compressed air or vacuum to desired positions, thus leading to increased size or cost of the imaging apparatus and also to the creation of noise. In order to avoid such drawbacks associated with such air-operated separating mechanisms there is also known a separating method utilizing a separating belt.
FIG. 1 shows, in a perspective view, the conventional separating method utilizing a separating belt, in which a transfer sheet P supplied to a photosensitive drum 1 is transported along the periphery thereof, while a side edge of said sheet is separated from the peripheral surface of the drum by means of a separating belt B. As said belt B is supported by the pulleys 5, 6, 7, 8 and 9 so as to be separated from the surface of drum 1 along a turn roller 2, the transfer sheet P is pinched at a side edge thereof between said separating belt B and turn roller 2 and is thus separated from the drum 1.
In said separation, however, as shown in FIG. 2, the opposite side edge of sheet P, being separated from the surface of a guide roller 2a provided adjacent to said turn roller 2, is left in a very unstable state and is delayed in advancement with respect to said pinched side edge. Consequently the transfer sheet P advances in a direction (represented by the arrow 3) different from the driving direction (represented by the arrow 4) of advancing rollers R, and the leading end of sheet P does not simultaneously reach said rollers R. For this reason the rollers R are unable to realize stable sheet advancement, thus frequently resulting in wrinkle formation and sheet jamming.
As explained in the foregoing, the diagonal advancement of transfer sheet is almost unavoidable in such separating method with a separating belt, though it is advantageous in the simplicity of mechanism and secure separating operation. Besides, the extent of said diagonal advancement strongly varies according to the stiffness of transfer sheet, adhesion of drum and said sheet, pinching force exerted on the sheet by the separating belt and roller etc. For this reason such a separating mechanism will result in frequent troubles such as sheet jamming or diagonal feeding and is unable to ensure satisfactory fixing or roller feeding in the succeeding step.